Conventional pliers (such as wire pliers) are formed in such a way that a pivot connects two members which include a jaw and a handle, respectively. In use, the jaw span (the space between two jaws for clamping objects) is adjustable only by operating the handles to rotate around the pivot, and the applicable range of the jaws is small. However, some types of pliers require the span adjustment of the jaws in use. For example, water pump pliers require the span adjustment of the jaws in accordance with the size of the pipe to be clamped.
To this end, pliers appear with a larger adjustable jaw span. Such technical scheme is also repeatedly recorded in patent documents, such as the Chinese Utility Model Patent being representative, entitled “Fast Locking Water Pump Pliers”, with the Authorized Publication Number being CN2790679Y and the Patent Number being ZL200520070493.2. The disclosed water pump pliers include a left member 101 and a right member 102, as shown in FIG. 16 and FIG. 17. The left member 101 is provided with a bar-shaped hole 113 in an open way. Both sides of the bar-shaped hole are provided with a rack 114. The right member 102 is provided with a hinged hole 123 in an open way. A hollow bolt 103 tightly fits a blind nut 104 through the bar-shaped hole 113 and the hinged holes 123. The hollow bolt 103 is axially provided with a hole 131 in the central part in an open way with a sliding part 105 arranged therein, and a gear 151 is arranged at the inner end of the sliding part. One end of a spring 106 is installed on the blind nut 104, while the other end is installed on the sliding part 105, so as to bias the sliding part in the predetermined working position. In the position, the gear 151 is engaged with the rack 114 of the left member 101, so that the hollow bolt 103 cannot slide within the bar-shaped holes 113 of the left jaw. The jaws will be opened and closed when the left and right members 101, 102 are operated at this time so as to clamp and twist objects. Now, under the effect of the bias force of the spring 106, the sliding part 105 is in an ejected state, and the button 107 at the external end thereof extends beyond the hollow bolt 103.
If the span of the jaws needs to be adjusted, the button 107 is pressed only, so that the sliding part 105 overcomes the bias force of the spring 106 to slide inwardly, and the gear 151 at the inner end of the sliding part 105 is disengaged from the rack 114. Now, the right member 102 can randomly slide in the bar-shaped holes 113 of the left member 101 along with the hollow bolt 103. When it is adjusted to the required position, the button 107 is released again. The sliding part 105 resets under the effect of the bias force of the spring 106. The gear 151 is re-engaged with the rack 114. The left and right members 101, 102 are repositioned, and the water pump pliers can be in normal use again.
In the configuration, no matter whether the jaw span is adjusted to be larger or to be smaller, the button needs to be pressed so that the gear is disengaged from the rack, which is inconvenient in operation. Specifically, the size of the object to be clamped cannot be estimated very accurately when being clamped and since the force can be best applied to the object to be clamped and it is most convenient and comfortable to use for hands only when the jaws is in the parallel position, it requires repeated adjustment in the actual use. In particular when working in some small or narrow spaces, It is possible that we cannot see the object to be clamped with our eyes, so we can only determine the best jaw span by making continuous attempts. And the pliers with the above configuration can be adjusted only after being pressed by hands. In many positions, hands cannot reach into the position proximate to the object, which makes it more troublesome. Thus we need to take the pliers out for adjustment and then put it in for another try. If it is not suitable, we should take it out again for adjustment. It is rather inconvenient in use.
Furthermore, though the spring enables the gear at the other end of the sliding part to engage with the rack of the left member, the spring can only keep the gear in place where the gear can engage with the rack, but the spring cannot ensure a reliable engagement between the gear and the rack. In use, the gear slips from the rack easily, which leads to the failure of the adjustment of the jaw span. In addition, there are so many parts in the configuration which makes the configuration complex.